Induction-motor.



PATBNTED DEC. 3, 1907. B. F. W. ALEXANDERSON.

INDUCTION MOTOR.

APPLIOATIOI FILED NOV. 9. 1005.

3 BEEETB8HEKT 1.

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v v 5 Wm; (L M25 W L X- No. 872,550. PATENTBD DEC O 1907.

. E.'F. W. ALEXANDERSON.

INDUCTION MOTOR.

APPLIOATIOI FILED 10V. 9. 1905.

3 SHEETS-SHEET 2.

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ATTORNEY UNITED STATES PATENT oFFIoE.

ERNST I. W. ALEXANDERSON, OF SCIIENECTADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION 01 NEW YORK.

INDUCTION-MOTOR.

Specification of Letters Patent.

Patented Dec. 3, 1907.

Applicatio as NovemberlQ, 1905. Serial No. 286,511.

To all whom. it may concern:

Be it known that l, Elms! F. W.v ALEX- ANDERSON, a subject of the Kingof Sweden, residing at Schenectady, county of Schenectady, State of NewYork, have invented certain new and useful improvements inInduction-Motors, of which the following is a specification. I

My invention relates to induction motors,

and its object is to provide a novel arrangedouble-throw switch in therimary circuit of the motor, and is especia lyadapted for remotecontrol.

It has been proposed heretofore to so ar,

range the rotor winding of an induction motor that it offers a lowresistance path for currents induced by one number of poles in theprimary and a high resistance path for currents induced by a differentnumber of primary poles, and to so arrangethe primary winding that itmay be connected for either number of poles. With this arrangement whenthe primary winding is connected for a number of poles corresponding tothe high resistance secondary path, the motor starts with resistance inthe rotor circuit;

'then after the motor has started, by changing the connections of theprimary winding so as to arrange it for the other number of poles,

cuited secondary. With this arrangement,

as heretofore employed, if the secondary 1s arranged to'ofl'er a lowresistance path for the smaller number of poles, then obviously themotor must be started with the primary connected for the greater numberof poles; and consequently unless the two numbers of oles are nearlyequal,-an arrangement which ordinaril requires a special winding orcomplicate terminal connections, or boththe motor will .run up, withresistance inthe secondary circuit, to a speed which is only a fractionof the normal speed when conthe motor runs as with a short-cir-' nectedfor the smaller number of poles. Consequently,when the primary circuitconnections are changed to establish the smaller number of poles, themotor must speed up with no reslstancein the secondary circuit. Themotor is thus likely to draw an excessive current and may exert a torqueat firstconsiderably less than its full-load torque. on

the other hand, if the motor is arranged to' offer a low resistance pathfor currents induced by the greater number of poles, then obviously themotor must be connected for the smaller number of poles at starting; andif this connection is maintained too long the motor will be brought upto a speed much higher than that at which it is intended to operate.

By my invention I so modify the connections of the primary winding thatthe motor may be started with the primary connected for a number ofpoles smaller than that at which the motor is designed to operate, sothat it will be brought up to its normal speed with a resistance in therotor circuit, but when it reaches approximately normal speed the torquecharacteristic of the motor will be such that it will be prevented frompassing above this speed, no matter how long the controlling switch ismaintained in starting position. I accomplish this result by soarranging the primary winding of the motor that'when it is connected forstarting it roduces simultaneously two dillerent num ers of poles. Owingto the difl'erence between the torque characteristics of an inductionmotor having a short-circuited rotor and one having a high resistance inthe rotor circuit, the portion of the rimary winding connected toproduce t io greater number of poles, which is the number for which thesecondary offers a low resistance path, exerts a practically negligibleeffect; so that the motor operates at starting substantially as thongwere in circuit. As the motor approaches the speed which is synchronousfor the greater number of poles, the torque due to the portion of thewinding connected for the greater number of poles begins to exert apreponderating effect, and when this speed is passed this portion ofthewinding has a generator action which serves automaticallyto reducethe resultant motor torque and prevent the motor from reaching a speedabove,

I only the other portion of the winding shifting the controlling switchto running position all the primary winding is connected for the greaternumber of poles and the motor then operates as an ordinaryshort-circuited induction mQ torK-Since the motor is operating atsubstantially synchronous speed when this change is made, the speed ofthe.

motor is not varied, and consequently no eX- cessive current is drawnfrom the source.

My invention then consists in the combination with an induction motor,of means for connecting the primary winding of the motor'for producingsimultaneously two different numbers of poles, the secondary of themotor being arranged to offer a low resistance path for the currentsinduced by one number of poles and a high resistance path for thecurrents induced by the other number of poles. v v i a My inventionfurther consists in connecting all of the primary winding for the numberof poles corresponding to the low resistance secondary path when themotor is up to speed.

My invention further comprises certain specific arrangements andconnections of the primary winding which render it possible to controlthe motor so as to obtain the above results with a simple double-throwswitch, and with a minimum number of terminal connections.

My invention further comp'rises the method of starting an inductionmotor of the type described above, which consists in connecting theprimary winding of the motor to produce two magnetizations ofydifferentpolenumbers simultaneously.

My invention further comprises a method of operatm an induction motor ofthe type described a ove, which consists in starting the motor byconnecting'the primary windmg of the motor to produce two differentnumbers of poles simultaneously, and when the motor is up to speedconnecting the primary winding to produce only the greater number ofpoles.

My invention will best be understood by reference to the accompanyingdrawings, in which Figure 1 shows diagrammatically the circuitconnections of the motor and its controlling switch; Fig. 2 is anexplanatory diagram of the motor torque characteristic; Flg. 3 shows adevelopment on a plane surface of the primary winding; Fig. 4 shows asimilar development of a singlephase of the and Fig, 5 shows a similardevelopwinding; ment of a portion of the secondary winding; Inconnecting the primary winding of the motor I divide each phase into twogroups,- thus, in Fig. 1, showing a three-phase motor, one phase isshown divided into the two groups A and D; a second phase into groups Band E, and the third into groups C and F. The corresponding groups A,and O of the three phases are shown connected in delta, while each ofthe other groups has one terminal connected to a central point on theother group of the same phase. Thus, group D has one terminal connectedto the central point of group A.- Groups D, E and F are each arranged toproduce the number of poles with which the motor is designed to operateunder normal running conditions. The groups A, B and C are each arrangedto pro duce the same number of poles as groups D, E and F, or a numberequal to one-half of the poles produced by the other groups, accordingto the direction of current-flow in these groups. Thus,,for instance, ifgroup Dis arranged toproduce eight poles, group A is so arranged thatwhen current flows through group D to the middle point of group A andthen outward in both directions to the terminals ofgrou A, group A willalso produce eight poles; ut if current is supplied to the terminals-ofgroup A, it will produce four poles.

The terminals 1,- 2, -3, of the delta formed by groups A, B and C andthe free terminals 4, 5, 6, of D, E and F are connected to a controllingswitch S. This controlling switch is arranged to connect the source ofthreephase current indicated by the line-wires L either to the terminals1, 2 and 3 of the delta, or to the free terminals 4, 5 and 6 of groupsD, E and F, and to short-circuit the set of terminals not connected tothe source.

In order to clearly show the circuit connections I have shown the switchas of the drumtype with its contacts develo ed on a plane surface. Inpractice a doub e-throw leveror knife switch might and preferably wouldbe employed, .and this switch may be prov vided with a spring to move itautomatically from starting position when released, as described inPatent No. 735,077, Everest. The

particular construction of controlling switch,

however, forms no part of my present invention. y

When the switch S is in its first or starting position three-phasecurrent is supplied to the delta terminals 1, 2 and 3.- This currentflowing through groups A, B and C produces four poles in the motor.Current also flows ,through groups'D, E and F, since their terminals 4,5and 6 are connected together so that these groups are in Y, andthe'currtnt that flows through these groups produces eight poles in theprimaryrmember, which exist simultaneously with the four poles produced.

by groups A, Band C.

The rotor is provided with a number of groups G, each of which is soarranged thatgroup, then through resistance H and back" to theterminals,that is, the secondary offers a low resistance path for aneight-pole connection and a high resistance path for the four-poleposition of the primary.

As has already been stated, the motor is so connected that at startingboth a fourpole and an eight-pole magnetization exists in the primarymember. The resultant effeet is the same as though the torques of afour-pole and eight-pole motor were superposed; the four-pole motorvbeing arranged with a high resistance in the rotor circuit and theeight-pole with a low resistance. The

torque relations are shown in Fi 9 which ba shows the speed torquecharacteristics for both the four-pole and the eight-pole portions ofthe primary winding. The curve (t represents the torque characteristicdue to the four-pole portion of the primary winding. This curve has thewell known characteristic. of an induction motor having a highresistance in the secondary circuit; starting with a high torque whichgradually diminishes becoming zero when synchronous s eed is reached,the synchronous speed for t e fourpole connection being indicated by theline 0 c. 1) represents the torque characteristic due to the eight-poleportion of the rimary winding at starting. This curve ms thecharacteristic of an induction motor with short-circuited secondary.Atstarting the torque due to the eight-pole portion of the winding ispractically negligible, as shown in the figure, but graduallyincreases-as it aproaches synchronism, falling abruptly again 111stbefore synchronism is reached. Synchronous speed for the eight-poleconnection is indicated by the line 0 (Z. In passing above thesynchronous speed the torque due to the eight-pole portion of thewinding becomes negative,that is, this portion of the winding has agenerator action and the maximum generator torque is greater than themaximum motor torque. Obviously, this negative torque of the eight-poleportion of the winding tends to balance the torque due to the four-poleportion and at some point, as ate, the distance of the curve 6 below theline, is equal to the distance of the curve a above the line, of zerotorque. That is,'the resultant torque at this point is zero.Consequently, with a given load the motor will au tomatically ceaseaccelerating at some speed below the point e; the particular speeddepending upon the load on the motor. It

will be noted that this speed is a proxi mately synchronous speed forthe eig t-pole connection, so that if t e portion of the winding whichat starting was connected for four poles is now connected for eightpoles, the speed of the motor will not be varied to any extent and themotor will operate as an ordinary eight-pole motor with ashort-circuited secondary.

The connections of the motor windings for obtaining the relations whichhave been described above are shown in Figs. 3 to 5. Fig. 3 shows adevelopment on a plane surface of the complete primary winding reducedto its simplest terms'of one coil per pole per phase, one phase beingindicated in heavy lines, another in dotted lines, and a third in li htlines. In order further to simplify the diagram and toavoid confusion,the end connections and terminals of the four-pole portion of thewinding are shown above the coils, and those for the eight-pole portionof the winding below the coils. The several terminals are numbered tocorrespond with Fig. 1. The arrangement of the primary winding will bestbe understood by referring to Fig. 4, which shows a single phase of theprimary with the four-pole and e'ight-pole portions separated from eachother. The direction of current in the windings at starting is indicatedby light arrow-heads and the polarities produced by this current-floware indicated by letters N and S in light lines. The current-flow withthe running connection is indicated by heavy arrow-heads, and thepolarities by letters in heavy lines. At starting the terminals 1 and 2of the group A are connected to the source, as is shown intFig. 1. Thecurrent at any instant may consequently be assumed as entering atterminal 1, passing through all the coils of group A in series, and outat terminal 2. This currentflow will produce four poles, as indicated bythe letters N and S in light lines. At the same time a current willexist in the group D, which will be approximately ninety degrees out ofphase with the current in group A, but the direction of which may beconsidered at any instant as indicated by the light arrowheads withresultant polarities shown by the reference letters in light lines. Thiscurrent produces eight poles, as shown, and. since-the relativedirection of current-[low through the coils of group D is never changedin operation, this group always produces eightpoles both at starting andin running. Thus, it will be seen that at starting two different numbersof poles oo-exist in the primary Winding,f0urpole magnetization due tothe current in group and'an eight-pole 'magnetization due to the currentin grou I). Now if the free terminal 4 of group D is connected to thesource, and the terminals 1 and 2 of groups A disconnected from thesource and connected together by a shortcircuit, current will flowthrough groups A and D, as indicated by the heavy arrows. It will beseen that this flow of current produces in group A an eight-polcmagnetization which assists the magnetization produced by group D,-thatis, all the coils of the phase are connected to produce an eightpolemagnetization.

Fig. 5 shows the arrangement of a portion of the rotor winding. Thisportion consists of a group of four coilswhich are connected in seriesin a closed circuit, 'with a resistance H connected between two pointsin its closed circuit in the manner indicated diagrammatically inFig. 1. If this closed circuit is sub' jected to a four-polemagnetization, as indicated by the letters N and S in light lines,currents will be induced which will flow in the direction indicated bythe light arrowheads. It will be seen that these currents must flowthrough the resistance H, so the closed circuit acts as a highresistance sec- A ondary for the four-pole magnetization. If, I

however, this same circuit is subjected to an eight-pole magnetization,as indicated by the letters N and S in :heavy lines, a current will beproduced corresponding in direction to the heavy arrow-heads, and thesecurrents flow around the closed circuit without pass ing through theresistance,that is, the closed circuit acts as a short circuit for theeight-pole magnetization. The rotor winding may 'be conveniently made upof a plurality of closed circuits similar to that shown in Fig. 5',distributed around the rotor core. I

While I have shown a convenient arrangement of circuit connections foraccomplishing the results desired, my invention is not limitedin itsbroad aspects to these particular connections. Consequently I do notdesire to limit m self to the construction and arrangement 0 parts hereshown, but aim in the appended claims to cover all modifications whichare within the scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is,-

1. In combination with an induction motor, means for connecting theprimary windmg of the motor for producing simultaneously differentnumbers of poles, the secondary of said 'motor being arranged to offer alow resistance path for currents induced by one number of poles and, ahigh resistance ath for currents induced by another numer of poles. v-2. In combination with an induction motor, means for connecting theprimary winding of the motor for producing simultaneously two differentnumbers ,of poles, the secondary of said motor being arranged to ofi'era low resistance path for currents induced by one number of poles and ahigh resistance path for currents induced by the other number of poles.

3. In combination with an induction motor, means for connecting theprimary winding of the motor for producing simultaneously two differentnumbers of poles, the secondary of said motor being arranged to offer alow resistance path for currents induced by the greater number of polesand a high resistance path for current induced by the smaller number ofpoles.

. 4. In combination with an induction motor, means for connecting twoportions of the primary winding of the motor for producingsimultaneously two different pole numbers bearing to each other theratio of one to two,

the rotor-winding being'arranged to offer a' low resistance path forcurrents induced by one number of poles and a high resistance patn forcurrents induced by the otherinumber of poles.

5. In combination with an induction motor, meansfor connecting twoportions of the 1 primary Winding of the motor for producingsimultaneously two different pole numbers bearing to each other theratio of one to two, the rotor-Winding being arranged to offer a lowresistance path for currents induced by the "greater number of poles anda high resistance path for currents induced by the smaller number ofpoles.

6.- In c ombination with an induction motor having a secondary adaptedto offer a high resistance path for currents induced by one number ofpoles and a low resistance path for currents induced by a second numerof poles, means for connecting a p'ortlon of the primary winding of themotor for each number of poles at starting, and means for connecting allof the primary winding for said second number of poles when the motorhas started.

7. In combination with an induction mo- .tor having a secondary adaptedto offer a high resistance path for currents induced by one number ofpoles. and a low resistance path for currents induced by a certaingreater number of poles, means for connecting a portion ofthe primarywinding of'the motor for each number of. poles at starting, and meansfor connecting all the primary Winding for the greater number of polesWhen the motor has started.

8. In combination with an induction motor having a secondary adapted toofle'r, a high resistance path for currents induced by one number ofpoles and a low resistance path for currents induced by double thatnumber of poles, means for connectmg a portion of the primary Winding ofthe motor for each number of poles at starting, and means for connectingall the primary winding or the double number ,of poles when the motorhas started.

9. In an induction motor, a primary member provided with a windingarranged to be connected to produce different numbers of olessimultaneously, and a secondary memher having its winding connected to ashortcircuiting connection and to ,a resistance in such a manner that itwill offer a low resist ance path for the currents induced by one numberof poles and a high resistance path for current-s induced by anothernumber of poles.

10. In an induction motor, a primary member provided with a windingcomprising two portions, one of said portions being arranged to reduce acertain number of poles and the ot ier portion being arranged to producethe same or a different number of poles according to its connection, anda secondary member having its winding connected to a shortcircuitingconnection and a resistance in such a manner that it will offer a lowresistance path for currents induced by one number of poles and a highresistance path for currents induced by another number of poles.

11. In an induction motor, a primary member provided with a windingarranged to be connected to produce different numbers of polessimultaneously, and a secondary member having its winding connected to ashort-circuiting connection and a resistance in such a manner that itwill offer a low resistance path for currents induced by one number ofpoles and a high resistance )ath for currents induced by a smallernumber of poles.

12 In an induction motor, a primary member provided with a windingcomprising two portions, one of said portions being arranged to producea certain number of poles and the other to produce the same or a smallernumber of poles according to its connection, and a secondary memberhaving its winding connected to a short-circuited connection anda'resistance in'such a manner that it offers a low resistance path forcurrents induced by the greater number of poles and a high resistancepath for currents induced by the smaller number of poles.

13. In an induction motor, a rimary winding having the coils of each pase divided into two groups, one of said groups having. a terminalconnected to an intermediate point on the other group, the latter groupbeing connected to produce one number of poles when traversed by currentfiowing from one terminal to the other of said group and a second numberof poles when group being connected to produce one number of poles whentraversed by current flowing from one terminal to the other of saidgroup and a second number of poles when traversed by current flowingfrom said intermediate point to both terminals, and the first-mentionedgroup being connected to produce said second number of poles.

15. In an induction motor, a primary winding comprising two portions,one of said portions being arranged to produce a certain number ofpoles, and the other portion being arranged to produce the same or adiil'erent number of poles according to its connection, and terminalleads for each of said portions.

16. In an induction motor, a primary winding having the coils ot eachphase divided into two groups, one of said groups being arranged toproduce the same number of )oles as theother group or a different numberaccording to its connection to the source,

' and switch contacts for varying said connection.

17. In a three-phase induction motor, a primary winding having the coilsof each phase divided into two groups, one group of each phase beingconnected with the corresponding groups of the other phases, and thesecond group of each phase having one terminal connected to the centralpoint of the first group of each hase, and means for connecting eitherthe ee terminals of the first group or the free terminals of the secondgroups to the source.

18. In a three-glhase induction motor, a primary winding aving the coilsof each phase divided into two groups, one group of each phase beingconnected with the correponding groups of the other hases, and thesecond group of each phase aving one terminal connected to the centralpoint of the first group of each phase, means for connectin g either thefree terminals of the first group on the free terminals of the secondgroups to the source, and Short-circuiting either set of terminals whennot connected to the source.

19. The method of starting an induction motor having a secondaryarranged to offer a low resistance path for currents induced by onenumber of primary poles and a high resistance ath for currents inducedby a lower number. of poles, which consists in connecting the primarywindin of the motor to produce both numbers ofpoIes simultaneously.

20. The method of operating an induction ing' to produceonly the greaternumber of 10 motor having a secondary arranged to offer a poles when themotor is up to speed. low resistance path for currents induced by Inwitness whereof, I have hereunto set one number 01f1 ofrimary poles sand3 lhigh my' hand this 8th day of November, 1905. 5 resistance at orcurrents in uce a Y lower numb er of poles, which consists in c dn- ERAST MEXMDERSON' necting the primary winding of. the motor to Witnesses:produce both numbers of poles simultane- BENJAMIN B. HULL, ously atstarting, and'connecting said wind-' MARGARET E. WOOLLEY.

